W3C home > Mailing lists > Public > www-rdf-logic@w3.org > January 2007

Re: weird example in RDF-MT document...

From: Axel Polleres <axel.polleres@urjc.es>
Date: Thu, 25 Jan 2007 22:18:28 +0100
Message-ID: <45B91EA4.5060109@urjc.es>
To: www-rdf-logic@w3.org
CC: Denny Vrandecic <dvr@aifb.uni-karlsruhe.de>

Hi denny,

Denny Vrandecic wrote:
> this makes sense to me. Consider the following addition of the graph:
> 
> _:xxx dc:creator ex:Axel.
> _:xxx dc:date "Jan-24-2007".
> _:yyy dc:creator ex:Denny.
> _:yyy dc:date "Jan-25-2007".
> 
> basically saying that the statement was done by you yesterday, and by me 
> today, you would not want to entail that it was said by you today as well.

sure, but this is not the point of the example in the spec.

1) Given the additional information you mention and lets call this graph 
S' :

  _:xxx rdf:type rdf:Statement .
  _:xxx rdf:subject <ex:subject> .
  _:xxx rdf:predicate <ex:predicate> .
  _:xxx rdf:object <ex:object> .
  _:yyy rdf:type rdf:Statement .
  _:yyy rdf:subject <ex:subject> .
  _:yyy rdf:predicate <ex:predicate> .
  _:yyy rdf:object <ex:object> .
  _:xxx <ex:property> <ex:foo> .
  _:xxx dc:creator ex:Axel.
  _:xxx dc:date "Jan-24-2007".
  _:yyy dc:creator ex:Denny.
  _:yyy dc:date "Jan-25-2007".

  Now this makes a difference of course, but even then, the graph S' 
still entails the graph E consisting of the single triple,

   _:yyy <ex:property> <ex:foo> .

(the blank node id in E isn't supposed to have any meaning in commong 
with _:yyy in the original graph).

it would though indeed not entail the graph E'

   _:yyy dc:creator ex:Denny.
   _:yyy dc:date "Jan-25-2007".
   _:yyy <ex:property> <ex:foo> .

Do you see my point now?
(looks like we jointly elaborated an example which makes more sense to 
me at least, but I still have problems with the original one in the spec...)


2) Note that the original graph S as in the example (without any 
additional triple):

  _:xxx rdf:type rdf:Statement .
  _:xxx rdf:subject <ex:subject> .
  _:xxx rdf:predicate <ex:predicate> .
  _:xxx rdf:object <ex:object> .
  _:yyy rdf:type rdf:Statement .
  _:yyy rdf:subject <ex:subject> .
  _:yyy rdf:predicate <ex:predicate> .
  _:yyy rdf:object <ex:object> .
  _:xxx <ex:property> <ex:foo> .

is not lean since

  _:xxx rdf:type rdf:Statement .
  _:xxx rdf:subject <ex:subject> .
  _:xxx rdf:predicate <ex:predicate> .
  _:xxx rdf:object <ex:object> .
  _:xxx <ex:property> <ex:foo> .

entails the whole graph. That is basically my problem with the example 
where I got stuck.

best,
axel




> One could discuss if the identity of a statement is constituted by its 
> three components, subject, predicate, object, but the standard clearly 
> says it does not, and so the identity of a statement seems constituted 
> by some other kind of magic (well, I'd go for an URI).


> This also has the advantage that a statement with an URI as its 
> identifier can actually be dynamic, like ex:Denny ex:listens_to 
> ex:Jewel, which changes from time to time -- but nevertheless it could 
> always have the same URI.
> 
> Cheers,
> denny
> 
> Axel Polleres wrote:
> 
>>
>> Hi all,
>>
>> I was studying the RDF semantics document once again in some detail 
>> and it looked to me I found a bug in an example in the end of section 
>> 3.3.1.
>> Since I doubt that, I was asking myself whether somebody here can help 
>> me to get the knot out of my head....
>>
>>
>>    http://www.w3.org/TR/rdf-mt/#Reif
>>
>>
>>
>> In the end of that section, it is stated that
>>
>> "For example,
>>
>> _:xxx rdf:type rdf:Statement .
>> _:xxx rdf:subject <ex:subject> .
>> _:xxx rdf:predicate <ex:predicate> .
>> _:xxx rdf:object <ex:object> .
>> _:yyy rdf:type rdf:Statement .
>> _:yyy rdf:subject <ex:subject> .
>> _:yyy rdf:predicate <ex:predicate> .
>> _:yyy rdf:object <ex:object> .
>> _:xxx <ex:property> <ex:foo> .
>>
>> does not entail
>>
>> _:yyy <ex:property> <ex:foo> ."
>>
>>
>>  This is at the very least strange for me...  and I think simply wrong.
>>
>> I mean, I understand what is *meant* to be said here, but of course
>> the single triple graph
>>
>> _:yyy <ex:property> <ex:foo> .
>>
>> IS entailed by the former.
>>
>> Can anybody shed light on me? I must admit that I have some 
>> difficulties to understand the non-normative reificaiton proposed in 
>> that section, but I would assume that simple entailments still hold.
>>
>> I would be grateful if anybody can shed light on me or tell me whether 
>> this was already answered elsewhere?
>>
>> Thanks,
>> axel
>>
>>
>>
>>
>>
> 
> 


-- 
Dr. Axel Polleres
email: axel@polleres.net  url: http://www.polleres.net/
Received on Thursday, 25 January 2007 21:24:29 UTC

This archive was generated by hypermail 2.3.1 : Wednesday, 2 March 2016 11:10:47 UTC